Carbonate Thermoluminescence From Meishan Section,Zhejiang Province And Its Implication For Environmental Changes During The Permian-Triassic Transition

The Permian-Triassic(P-Tr)crisis was the largest mass extinction of the Phanerozoic,which eliminated over 90% of marine species This event was likely attributed to the eruption of the Siberian Traps and associated environmental changes,such as oceanic anoxia and global warming.The whole ecosystem suffered mass destruction and biodiversity of marine invertebrates was dramatically reduced and remained low during the Early Triassic.However,how primary productivity changed during this extinction event and its aftermath remains controversial.Carbonate thermoluminescence(TL),as a traditional technique for Quaternary chronology,has been used for paleo-environmental research and can be a potential proxy for marine primary productivity.The Meishan section,the Global Stratotype Section and Point(GSSP)of the Permian-Triassic boundary,has been studied well with large amounts of geochemical data.We choose this section to carry out TL measurements because of its good research basis.Chemical measurements about element abundances,carbon and oxygen isotope have also been taken out in order to analyze the TL signals and its potential implication for marine productivity change during the P-Tr transition.Many discussions depending on Mn and Sr contents,carbon and oxygen isotope,and cathodoluminescence,have been carried out to recognize the influence of diagenesis.The analyzation indicate samples from Meishan section may preserve the primary carbonate TL signal despite potential diagenetic alteration.Carbonate TL peak intensity is mainly controlled by the Mn contents substituted in calcite lattices.There show two major variations in TL peak intensities during the P-Tr transition.The first variation is interpreted to record periodic fluctuations on a Milankovitch scale(~20-kyr rhythm).The periodic variations of TL are negatively correlated with Mn concentrations,suggesting primary productivity is a key factor controlling the TL peak intensity by photo-reduction of particulate Mn in the presence of organic matter.Therefore,the periodic fluctuations of TL were likely controlled by primary productivity changes on orbital timescales.The second variation is characterized by a rapid increase across the P-Tr boundary,which represents the rapid increase rise of dissolved Mn in shallow water.Increased dissolved Mn may be contributed to enhanced marine productivity and/or oceanic anoxia.Carbonate TL possibly indicates higher primary productivity in the Early Triassic ocean.